Light reflective substrate and light emitting device using the same

ABSTRACT

An object of the present invention is to provide a light reflective substrate capable of achieving high optical reflectance even though fine particles are not used as a material, and a light emitting device using the same. The light reflective substrate according to the present invention comprises: a glass matrix; and RNb 2 O 6  crystal and/or R 4 Nb 2 O 9  crystal (R is at least one of Mg, Ca, Sr and Ba) in the glass matrix.

TECHNICAL FIELD

The present invention relates to a light reflective substrate havinghigh optical reflectivity and a light emitting device using the same.

BACKGROUND ART

LED and an organic EL device consume less electricity, and recentlyattract the attention as a new lighting device. In a device forlighting, a substrate and a package material, having high opticalreflectance are required in order to effectively utilize light emittedfrom a luminous body. For example, alumina ceramic having relativelyhigh optical reflectance, or a substrate having provided on the aluminaceramic an light reflective film comprising a metal has been used as theconventional package material of LED element. However, opticalreflectance of a substrate and a package material is required to befurther improved in order to obtain sufficient quantity of light asautomotive lighting, display lighting and general lighting.

To achieve the above object, Patent Document 1 describes a lightreflective substrate obtained by sintering a mixture of a glass powderand a ceramic powder, as a substrate having relatively high opticalreflectivity. Specifically, the light reflective substrate described inPatent Document 1 comprises glass-ceramic containing a glass powder anda ceramic powder, wherein in a cross-section of the glass-ceramic, anarea occupied by particles having a particle diameter of from 0.3 to 1μm of the ceramic particles is from 10 to 70%. Thus, in Patent Document1, high optical reflectivity is achieved by containing a large amount ofceramic particles having very fine particle size in the substrate.

CITATION LIST Patent Document

Patent Document 1: JP-A-2007-121613

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Light reflective substrate is obtained by, for example, forming amixture of a glass powder and a ceramic powder into a slurry, formingthe slurry into a green sheet, and firing the green sheet obtained.However, when a large amount of fine particles is contained in asubstrate as in the light reflective substrate described in PatentDocument 1, problems on production occur such that fluidity of thepowder is deteriorated, and forming of a green sheet becomes difficultto be conducted.

The present invention has been made in view of the above circumstances,and has an object to provide a light reflective substrate capable ofachieving high optical reflectance even though fine particles are notused as a material, and a light emitting device using the same.

Means for Solving the Problems

The present inventors found that high optical reflectance can easily berealized by containing specific crystals having high refractive indexcharacteristics in a glass matrix, and proposes the finding as thepresent invention.

That is, the present invention relates a light reflective substratecomprising: a glass matrix; and RNb₂O₆ crystal and/or R₄Nb₂O₉ crystal (Ris at least one of Mg, Ca, Sr and Ba) in the glass matrix.

Refractive index of RNb₂O₆ crystal and R₄Nb₂O₉ crystal is from 2.07 to2.20, and those crystals have very high refractive index as comparedwith that of the other conventional oxide crystals. On the other hand, arefractive index of a glass generally used as a light reflectivesubstrate is generally from 1.5 to 1.6, and therefore, refractive indexdifference between a glass phase and a crystal phase can be increased.As a result, light reflectance on a surface of a light reflectivesubstrate can remarkably be improved.

Secondly, the light reflective substrate of the present invention ischaracterized that R is Ca.

Thirdly, the light reflective substrate of the present invention ischaracterized that the content of RNb₂O₆ crystal and/or R₄Nb₂O₉ crystalis 0.3% by mass or more.

Fourthly, the light reflective substrate of the present invention ischaracterized to comprise a sintered body of a mixed powder containing aglass powder and RNb₂O₆ crystal and/or R₄Nb₂O₉ crystal powders.

According to the constitution, a light reflective substrate whereinRNb₂O₆ crystal powder and/or R₄Nb₂O₉ crystal powder is uniformlydispersed in a glass matrix can easily be produced.

Fifthly, the light reflective substrate of the present invention ischaracterized to comprise a sintered body of a mixed powder containing aglass powder containing at least RO as a composition, and an Nb₂O₅powder.

According to the constitution, a glass powder and an Nb₂O₅ powder arereacted to each other to crystallize RNb₂O₆ and/or R₄Nb₂O₉. As a result,light-absorbing defects are difficult to be foamed in an interfacebetween those crystals and the glass matrix. Therefore, light scatteringcan be enhanced, and as a result, optical reflectance can be enhanced.

Sixthly, the light reflective substrate of the present invention ischaracterized to further comprise at least one ceramic powder selectedfrom alumina, quartz, zirconia, titanium oxide, forsterite, cordierite,mullite and zircon.

According to the constitution, mechanical strength of the lightreflective substrate can further be improved.

Seventhly, the light reflective substrate of the present invention ischaracterized that the content of the ceramic powder is from 0.1 to 75%by mass.

Eighthly, the light reflective substrate of the present invention ischaracterized to have average optical reflectance at a wavelength offrom 400 to 800 nm of 80% or more.

Ninthly, the present invention relates to a light emitting device usingany one of the light reflective substrate described above.

Tenthly, the present invention relates to a light reflective substratematerial, comprising a mixed powder containing a glass powder, andRNb₂O₆ crystal powder and/or R₄Nb₂O₉ crystal powder (R is at least oneof Mg, Ca, Sr and Ba).

Eleventhly, the present invention relates to a light reflectivesubstrate material, comprising a mixed powder containing a glass powdercontaining at least RO (R is at least one of Mg, Ca, Sr and Ba) as acomposition, and Nb₂O₅ powder.

Twelfthly, the light reflective substrate material of the presentinvention is characterized that the R is Ca.

Thirteenthly, the present invention relates to a green sheet for a lightreflective substrate, using any one of the light reflective substratematerial above.

MODE FOR CARRYING OUT THE INVENTION

The light reflective substrate according to the present inventioncomprises: a glass matrix; and RNb₂O₆ crystal and/or R₄Nb₂O₉ crystal (Ris at least one of Mg, Ca, Sr and Ba) in the glass matrix.

It is preferable that total content of RNb₂O₆ crystal and R₄Nb₂O₉crystal in the light reflective substrate is 0.3% by mass or more, 1.0%by mass or more, and particularly, 1.5% by mass or more. When thecontent of RNb₂O₆ crystal and R₄Nb₂O₉ crystal is less than 0.3% by mass,sufficient optical reflectance is difficult to be obtained. On the otherhand, the upper limit is not particularly limited. However, excessivelylarge content of RNb₂O₆ crystal and R₄Nb₂O₉ crystal is not preferredfrom the standpoint of production costs. Therefore, it is preferablethat the content of RNb₂O₆ crystal and R₄Nb₂O₉ crystal is 30% by mass orless, 20% by mass or less, and particularly, 10% by mass or less.

Particle diameter of RNb₂O₆ crystal and R₄Nb₂O₉ crystal is notparticularly limited. However, good optical reflectance can be obtainedeven at short wavelength in the vicinity of, for example, 400 nm withdecreasing the particle diameter. On the other hand, an interfacebetween the crystals and a glass matrix is decreased with increasing thecrystal particle diameter, resulting in decrease in optical reflectance.From the standpoint of this, it is preferable that the crystal particlediameter is 10 μm or less, 5 μm or less, and particularly, 1 μm or less.As described before, in the case that the crystal particle diameter issmall, fluidity of a powder is deteriorated, and green sheet formingtends to be difficult. Therefore, special attention is needed such thatthe crystal content is not excessive.

The light reflective substrate of the present invention can be producedby a method of sintering a material for a light reflective substrate,comprising a mixed powder containing RNb₂O₆ crystal powder and/orR₄Nb₂O₉ crystal powder synthesized by, for example, a solid phasereaction, and a glass powder (production method 1). According to themethod, a light reflective substrate wherein the RNb₂O₆ crystal powderand/or the R₄Nb₂O₉ crystal powder is uniformly dispersed in the glassmatrix can easily be produced.

Alternatively, the light reflective substrate of the present inventioncan be produced by a method of sintering a material for a lightreflective substrate, comprising a mixed powder containing anRO-containing glass powder and Nb₂O₅ powder, and simultaneouslycrystallizing RNb₂O₆ and/or R₄Nb₂O₉ (production method 2). Particularly,according to the production method 2, a process of previouslysynthesizing RNb₂O₆ crystal powder and/or R₄Nb₂O₉ crystal powder can beomitted, leading to excellent mass productivity. Furthermore, in theproduction method 1, defects are liable to remain in the interfacebetween the glass powder and the crystal powder. This becomes a factorof light absorption, and optical reflectance tends to be decreased.

However, in the production method 2, light-absorbable defects aredifficult to be formed in the interface between a glass matrix andcrystal particles. Therefore light scattering can be enhanced, and as aresult, optical reflectance can be enhanced.

Examples of the glass powder that can be used in the present inventioninclude SiO₂—B₂O₃—Al₂O₃ glass, and SiO₂—B₂O₃—R′₂O (R′ is at least one ofLi, Na and K) glass.

The SiO₂—B₂O₃—Al₂O₃ glass preferably contains, in terms of % by mass asa composition, from 30 to 70% of SiO₂, from 10 to 40% of RO (R is atleast one of Mg, Ca, Sr and Ba), from 2 to 20% of B₂O₃, and from 2 to20% of Al₂O₃.

The reason for limiting the glass composition as above is as follows.

SiO₂ is a component of increasing chemical durability. It is preferablethat SiO₂ content is from 30 to 70%, from 40 to 70%, and particularly,from 45 to 60%. When the SiO₂ content is less than 30%, weatherabilitytends to be remarkably deteriorated. On the other hand, when the SiO₂content is more than 70%, a glass tends to be difficult to melt.

RO is a component for decreasing a liquidus temperature of a glass andadjusting meltability. It is preferable that RO content is from 10 to40%, from 10 to 30%, and particularly, from 15 to 30%, in total. Whenthe RO content is less than 10%, a melting temperature is too high. Onthe other hand, when the RO content is more than 40%, devitrification iseasy to occur.

Preferable range of the content of each component of RO is as follows.That is, it is preferable that CaO content is from 10 to 40%, from 10 to30%, and particularly, from 15 to 30%. It is preferable that the contentof each of MgO, SrO and BaO is from 10 to 40%, from 10 to 30%, andparticularly, from 15 to 20%.

B₂O₃ is a component of improving meltability of a glass and decreasing aliquidus temperature. It is preferable that the B₂O₃ content is from 2to 20%, from 2 to 15%, and particularly, from 4 to 13%. When the B₂O₃content is less than 2%, not only meltability of a glass isdeteriorated, but a liquidus temperature is increased, and as a result,devitrification easily occurs when forming a glass. On the other hand,when the B₂O₃ content is more than 20%, weatherability of a glass tendsto be decreased.

Al₂O₃ is a component of improving meltability and weatherability of aglass.

It is preferable that the Al₂O₃ content is from 2 to 20%, andparticularly, from 2.5 to 18%. When the Al₂O₃ content is less than 2%,meltability of a glass is easily deteriorated. On the other hand, whenthe Al₂O₃ content is more than 20%, devitrification easily occurs.

The SiO₂—B₂O₃—R′₂O (R′ is at least one of Li, Na and K) glass preferablycontains, in terms of % by mass as a composition, from 40 to 75% ofSiO₂, from 10 to 30% of B₂O₃, and from 0.5 to 20% of R′₂O.

The reason for limiting the glass composition as above is as follows.

SiO₂ is a network former of a glass. It is preferable that the SiO₂content is from 40 to 75%, and particularly, from 50 to 70%. When theSiO₂ content is less than 40%, vitrification is difficult to occur. Onthe other hand, when the SiO₂ content is more than 75%, a glass tends tobe difficult to melt.

B₂O₃ is a component of improving meltability of a glass. It ispreferable that the B₂O₃ content is from 10 to 30%, and particularly,from 15 to 25%. When the B₂O₃ content is less than 10%, a glass isdifficult to melt. On the other hand, when the B₂O₃ content is more than30%, weatherability tends to be decreased.

R′₂O is a component of improving meltability of a glass. The R′₂Ocontent is from 0.5 to 20%, and preferably from 3 to 15%. When the R′₂Ocontent is less than 0.5%, meltability of a glass tends to be remarkablydeteriorated. On the other hand, when the R′₂O content is more than 20%,weatherability is easily decreased.

Any of the glass composition can contain P₂O₅, MgO, ZnO, ZrO₂, otheroxide components, halide components, nitride components, and the like,other than the above components. Furthermore, the SiO₂—B₂O₃—R′₂O glasscan contain BaO and SrO. However, the total content of those othercomponents is preferably limited to 20% or less.

Average particle diameter D₅₀ of the glass powder is not particularlylimited. However, when the average particle diameter D₅₀ is too large,optical reflectance and mechanical strength of a light reflectivesubstrate are easily decreased. Therefore, the average particle diameterD₅₀ is preferably 15 μm or less, and particularly preferably 7 μm orless. On the other hand, when the average particle diameter D₅₀ is toosmall, production costs are increased. Therefore, the average particlediameter D₅₀ is preferably 0.5 μm or more, and particularly preferably1.5 μm or more.

The light reflective substrate of the present invention can contain aceramic powder as a filler in order to increase mechanical strength,other than RNb₂O₆ crystal and R₄Nb₂O₉ crystal. Examples of the ceramicpowder include alumina, quartz, zirconia, titanium oxide, forsterite,cordierite, mullite and zircon. Those can be used alone or as mixturesof two kinds or more thereof.

It is preferable that the content of the ceramic powder in the lightreflective substrate is from 0.1 to 75% by mass, from 2 to 75% by mass,and particularly, from 20 to 50% by mass. When the ceramic powdercontent is less than 0.1% by mass, an effect of increasing mechanicalstrength is difficult to achieve. On the other hand, when the ceramicpowder content is more than 75% by mass, many pores are generated in thelight reflective substrate, and mechanical strength is easy to bedecreased.

The light reflective substrate of the present invention is produced bypreforming a raw material powder containing a glass powder (material forlight reflective substrate) into various forms such as a plate form, asheet form and a block form, and then firing.

As the preforming method, various methods can be selected. Examples ofthe preforming method include a green sheet (tape) forming method, aslip casting method, a screen printing method, a mold pressing method,an aerosol deposition method, a spin coating method, and a die coatingmethod.

The green sheet forming method is a method of adding a resin binder, aplasticizer and a solvent to a raw material powder, kneading theresulting mixture to prepare a slurry, and preparing a green sheet(tape) from the slurry using a sheet forming machine such as a doctorblade. This method is in widespread use as a method for producing aceramic laminated circuit board. According to this method, in producinga ceramic laminated circuit board having optical reflective function by,for example, laminating a green sheet, it is easy to form a circuit in aboard, to embed a metal material having high thermal conductivity byforming an electric via-hole, or to form a heat discharge passage by athermal via-hole.

The screen printing method is a method of adding a resin binder and asolvent to an inorganic powder, kneading the resulting mixture toprepare a paste having a certain level of high viscosity, and forming afilm on a surface of a substrate using a screen printing machine.According to this method, a light reflecting portion of a specificpattern can easily be formed on the surface of a substrate. Furthermore,a film having a desired thickness of from about several microns to aboutseveral hundred microns can be formed by adjusting viscosity of a paste,thickness of a screen, the number of printing, and the like.

It is preferable that average optical reflectance at a wavelength offrom 400 to 800 nm of the light reflective substrate of the presentinvention is 80% or more, 85% or more, and particularly, 88% or more.

A light-permeable functional layer can be provided on a surface of thelight reflective substrate of the present invention. For example, aprotective coating against scratches, stain and chemical corrosion, anda functional layer having a function as a wavelength filter, opticaldiffusion or an interference layer can be further formed whilemaintaining optical reflective function on the surface of the lightreflective substrate.

The functional layer is not particularly limited, and conventionalmaterials such as glasses such as silicate glass; metal oxides such assilica, alumina, zirconia, tantalum oxide and niobium oxide; and resinssuch as polymethyl methacrylate, polycarbonate and polyacrylate can beused.

EXAMPLES

The present invention is described below by reference to Examples.However, the invention is not construed as being limited to thoseExamples.

Tables 1 and 2 show Examples and Comparative Examples.

TABLE 1 Example Comparative Example 1 2 3 4 1 2 3 Glass powder SiO₂ 5540 50 60 55 40 50 composition Al₂O₃ 14 10 14 10 (% by mass) B₂O₃ 6 15 2025 6 15 20 MgO 2 2 CaO 23 30 23 30 BaO 5 5 ZnO 3 5 3 5 Li₂O 2 6 2 Na₂O 25 9 2 5 K₂O 3 5 3 5 TiO₂ 2 2 ZrO₂ 2 2 P₂O₅ 1 1 Raw material Glass 68.496 57 61 70 75 60 powder powder composition CaNb₂O₆ 2 (% by mass)Ca₄Nb₂O₉ 3 2 Nb₂O₅ 1.6 4 Alumina 30 30 Zirconia 40 40 Mullite 35 Quartz25 High refractive index CaNb₂O₆ CaNb₂O₆ Ca₄Nb₂O₉ CaNb₂O₆ None None Nonecrystal (2) (5) (3) (2) *( ) means content Ca₄Nb₂O₉ (% by mass) (2)Optical reflectance (%) 90 88 82 90 78 75 72

TABLE 2 Example 5 6 7 8 Glass powder SiO₂ 50 50 55 58 composition Al₂O₃14 5 4 (% by mass) B₂O₃ 11 10 15 25 MgO 10 CaO 15 20 SrO 7 4 BaO 6 10Li₂O 2 4 Na₂O 2 5 5 K₂O 3 5 TiO₂ 2 ZrO₂ 2 P₂O₅ 1 Raw material Glass 6796 77 76 powder powder composition CaNb₂O₆ 2 (% by mass) Ca₄Nb₂O₉ 3 2Nb₂O₅ 3 4 Alumina 30 Zirconia 20 Mullite Quartz 20 High refractive indexMgNb₂O₆ (1) CaNb₂O₆ (2) Ca₄Nb₂O₉ (3) CaNb₂O₆ (2) crystal CaNb₂O₆ (2)SrNb₂O₆ (1) BaNb₂O₆ (1) Ca₄Nb₂O₉ (2) *( ) means content BaNb₂O₆ (1)SrNb₂O₆ (1) (% by mass) Optical reflectivity (%) 91 89 85 91

Light reflective substrate of each of Examples and Comparative Exampleswas produced as follows. Raw materials were formulated so as to obtainglasses having compositions shown in Tables 1 and 2, and melted in anelectric furnace kept at from 1,400 to 1,600° C. for 2 hours. The moltenglass obtained was poured in water-cooled rollers to obtain afilm-shaped glass. The glass film was pulverized with alumina ball millto obtain a glass powder (average particle diameter D₅₀=3 μm).

Various inorganic powders were mixed with the glass powder inproportions shown in Tables 1 and 2. The resulting mixed powder waspress molded with a mold having a diameter of 20 mm to prepare columnarpellets. The pellets were fired at 950° C. for 2 hours to obtain a lightreflective substrate.

The content of RNb₂O₆ crystal and R₄Nb₂O₉ crystal in the lightreflective substrate obtained was calculated based on peak intensity bypowder X-ray diffraction.

Optical reflectance of the light reflective substrate obtained wasmeasured. The results are shown in Tables 1 and 2. The opticalreflectance was evaluated by average optical reflectance at a wavelengthof from 400 to 800 nm measured by spectrophotometer.

As shown in Tables 1 and 2, the light reflective substrates of Examples1 to 8 contain RNb₂O₆ crystal or R₄Nb₂O₉ crystal, having high refractiveindex, and therefore had high reflectance of 82% or more. On the otherhand, the light reflective substrates of Comparative Examples 1 to 3 hadlow optical reflectance of from 72 to 78%.

Although the present invention has been described in detail and byreference to the specific embodiments, it is apparent to one skilled inthe art that various changes or modifications can be made withoutdeparting the spirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2010-041461filed Feb. 26, 2010 and Japanese Patent Application No. 2011-28031 filedFeb. 14, 2011, the disclosures of which are incorporated herein byreference in their entities.

INDUSTRIAL APPLICABILITY

The light reflective substrate of the present invention has very highoptical reflectance, and is therefore suitable for uses as a lightreflective substrate used in displays such as LED package and organicEL, automotive lighting, general lighting and the like.

1-10. (canceled)
 11. A light reflective substrate material, comprising amixed powder containing a glass powder containing at least RO (R is atleast one of Mg, Ca, Sr and Ba) as a composition, and Nb₂O₅ powder. 12.The light reflective substrate material according to claim 11, whereinthe R is Ca.
 13. A green sheet for a light reflective substrate, usingthe light reflective substrate material according to claim
 12. 14. Agreen sheet for a light reflective substrate, using the light reflectivesubstrate material according to claim 11.